A radio communication system employing LTE (Long Term Evolution) uses OFDMA (Orthogonal Frequency Division Multiplexing Access) for a downlink communication from a radio base station to a radio terminal and SC-FDMA (Single Carrier Frequency Division Multiple Access) for an uplink communication from a radio terminal to a radio base station. These multiplexing schemes implement user multiplexing by allocating radio channels in two dimensions, i.e., frequency and time.
In order to efficiently transmit data to multiple radio terminals in a communication area, a radio base station performs packet scheduling on each radio terminal, and assigns thereto an uplink radio channel and a downlink radio channel.
In addition, in order to notify a radio terminal of the assignment of radio channels to an uplink and a downlink, a radio base station needs to transmit information for assignment control of an uplink radio channel (uplink assignment control information) and information for assignment control of a downlink radio channel (downlink assignment control information) by using PDCCH (Physical Downlink Control CHannel) being a radio channel for control information in a downlink. However, since the resources for PDSCH (Physical Downlink Shared CHannel) being a radio channel for user information in a downlink need to be sufficiently reserved, a few resources are left for PDCCH. For this reason, when the uplink assignment control information and the downlink assignment control information are to be assigned to a logical area of PDCCH, cooperation and negotiation between assignment processing of uplink assignment control information and assignment processing of uplink assignment control information are required to prevent one-sided assignment.
Additionally, in radio communication techniques in recent years, retransmission in the occurrence of transmission error has been an important problem. As for this problem, an error correction technique called hybrid automatic repeat request (HARQ) in a lower layer is introduced. HARQ is a technique in which automatic repeat request (ARQ) and error detection using forward error correction code (FEC) are combined with each other to improve error detection capability in a receiving apparatus.